Method for recovering noble metals and other byproducts from ore

ABSTRACT

Method for the recovery of noble metals comprising the steps of subjecting ore particles to an electrolytic bath enhanced by an ultrasonic bath, the electrolytic bath comprising heavy and/or semi-heavy water; shock heating the ore particles for disintegrating them; and separating noble metals from the remains of said disintegrated ore particles.

The present invention relates to a method for recovering noble metals and other byproducts from ore. The present invention relates in particular to a method for recovering noble metals and other byproducts by disintegration of ore using nontoxic processes.

There are several methods for recovering noble metal from ore, which all have different drawbacks in terms of costs, recovery rate and/or environmental safety. These methods for recovering noble metal from ore include for example:

1 Fire Assaying—used usually for laboratory tests; requires expensive, long and complicated processing and even though the accuracy and recovery rate are very high, it is not an economical method.

2 Gravity Concentration of Ore—this method is relatively inexpensive, nontoxic, but the recovery rate is low, around 30%.

3 Leaching—is a relatively cheap recovery method with a recovery rate of around 50%, using toxic substances such as mercury, cyanide, strong acids, etc.

4 Smelting—not an economical method using high temperatures that are not easy to achieve; not economical if applied to an industrial scale, even though the recovery rate is high at around 95%; uses toxic substances and produces toxic gases during the processing.

5 Electrochemistry—has a high recovery rate of up to 98% but is a slow process, which makes it uneconomical for the recovery of noble metals from ore.

6 Roasting/sintering—not an economical method requiring further technologies to achieve the recovery of noble metals; toxic method producing toxic gases during processing.

7 Thermite—not an economical method even though the recovery rate is very high at around 99%; toxic process.

8 Hydrogen Reduction—very expensive processing with a recovery rate of around 50% with no industrial applicability; comprises an explosive dangerous process.

9 Recovery methods like application of colloidal chemistry, mechanical attrition, crystal growth, metallophilicity are used in scientific experiments only and don't have any industrial applicability.

An aim of the present invention is thus to propose an industrially applicable method for recovering noble metals and other byproducts from ore allowing for a high recovery rate.

Another aim of the present invention is to propose an industrially applicable and economical method for recovering noble metals and other byproducts from ore

Still another aim of the present invention is to propose an industrially applicable method for recovering noble metals and other byproducts from ore that doesn't use nor produce any toxic substance.

These aims are achieved by a method for recovering noble metals and other byproducts from ore comprising the features of the independent claim.

These aims are achieved in particular by a method for the recovery of noble metals comprising the steps of subjecting ore particles to an electrolytic bath enhanced by an ultrasonic bath, the electrolytic bath comprising heavy and/or semi-heavy water; shock heating the ore particles for disintegrating them; and separating noble metals from the remains of said disintegrated ore particles.

The method of the invention for recovering noble metals and other byproducts from ore is economical applicable at an industrial scale. Experiments have shown that it has a typical recovery rate of 95 to 99.9%. No toxic substance is used or produced during any step of the method.

The method of the invention will be better understood by reading the following description of a preferred embodiment, with the help of the figures, where:

FIG. 1 schematically illustrates an electrolytic bath placed inside an ultrasonic bath for performing a step of the method according to a preferred embodiment of the invention;

FIG. 2 schematically illustrates a crucible placed in a microwave oven for performing another step of the method according to a preferred embodiment of the invention;

FIG. 3 schematically illustrates a cone shaped container placed in an ultrasonic bath for performing still another step of the method according to a preferred embodiment of the invention.

The method of the invention for the recovery of noble metals and other byproducts from ore preferably comprises the following steps:

-   -   in an optional preliminary step, the ore is prepared for the         following steps of the method, which includes crushing the ore         to particles of a target mean size; the preliminary step uses         for example commonly known mechanical techniques for crushing         the ore;     -   in a next step, the crushed ore is placed in an electrolytic         bath that is placed in an ultrasonic bath; as explained below,         the substances necessary for performing the next step of the         method are produced by the electrolytic bath and penetrate into         the macro and micro pores of the ore with the help of the         ultrasonic bath;     -   in a following step, the ore is disintegrated using shock         heating, preferably microwave shock heating;     -   the noble metals are then recovered from the disintegrated ore,         using preferably an ultrasonic induced gravity separation         process.

The method of the invention for recovering noble metals and other byproducts from ore is preferably performed on small particles of crushed ore.

In an optional preliminary step of the method of the invention, the ore is thus crushed down to a predetermined target particle size, which participates to an increased efficiency of the next steps of the method of the invention for maximizing the recovery rate achieved with the method of the invention. The target size for the ore particles is preferably smaller than or equal to 590 microns (30 US Mesh), more preferably smaller than or equal to 420 microns (40 US Mesh), even more preferably smaller than or equal to 250 microns (60 US Mesh). Crushing of the ore is performed using any appropriate, preferably mechanical, method.

Optionally, the crushed ore is further centrifuged in order to create micropores and/or cracks or macropores in the ore particles and/or in order to further open micropores and/or cracks or macropores made in the ore particles during crushing.

According to the invention, the preferably crushed ore is placed in an electrolytic bath and simultaneously submitted to ultrasounds.

According to a preferred embodiment schematically illustrated in FIG. 1, the ore particles are placed in two ore containers 30 that are immersed at a distance from each other in an electrolytic bath 1. The external walls of the ore containers 30 are preferably permeable to the ions of the electrolytic bath. In a preferred embodiment, the external walls of the containers 30 are made of a microporous nylon membrane. The ore containers 30 are preferably cone shaped for an improved efficiency of the method of the invention. Other shapes are however possible within the frame of the invention.

An electrode 3 is located in each ore container 30. The electrodes 3 are electrically connected to a source of electrical power, which is not represented on the figures. The electrodes 3 are for example made of titanium or nickel and preferably have both the same shape and size. The electrodes 3 are preferably metallic rods that are located vertically along the central axis of their respective ore container 30. Other shapes and configurations of the electrodes are however possible within the scope of the invention. Each electrode may for example comprise several branches that are spread within their respective ore container.

According to the invention, the electrolytic bath 1 is placed in an ultrasonic bath 2, in which ultrasounds are generated that propagate through the walls of the electrolytic bath container 10 and into the electrolytic bath 1. The temperature of the ultrasonic bath 2 is preferably around eighty degrees Celsius.

The composition of the electrolytic bath 1 preferably includes heavy and/or semi-heavy water, such as for example deuterium or tritium. The concentration of heavy and/or semi-heavy water in the electrolytic bath 1 is for example between 2 to 5 percents.

The composition of the ultrasonic bath 2 is for example essentially water and/or any liquid in which ultrasounds efficiently propagate. The ultrasounds are preferably generated by one or more ultrasonic transducers located preferably inside the ultrasonic bath container 20, which are not shown on the figures for the sake of readability and conciseness.

The electrolytic processing of the ore is initiated by applying direct current (DC) voltage to the electrodes 3, for example six volts DC voltage with a current density of six amperes per square decimeter (A/dm²). One of the electrodes 3 becomes the anode, while the other electrode 3 becomes the cathode. Preferably, the polarity of the DC voltage is inversed at regular intervals in order to submit the ore contained in both ore containers 30 to the same treatment, i.e. to the same polarities for equivalent periods of time. The DC voltage is for example applied to the electrodes 3 for a total of two hours, divided in four cycles of thirty minutes each. After each cycle of thirty minutes, the polarity of the DC voltage is changed, i.e. after each cycle of thirty minutes, the cathode becomes the anode and vice versa.

When an electrical potential difference is generated between the electrodes 3 by applying the DC voltage, substances including chlorine, hydrogen, heavy water and reactive metal alkalines are produced in the electrolytic bath 1 near the electrodes 3. These substances produced in the electrolytic bath 1 at least partly penetrate the ore particles that are contained in the ore containers 30 and immersed in the electrolytic bath 1. According to the invention, the effects of the electrolytic processing of the ore is enhanced by the ultrasonic bath 2, in that the ultrasounds produced in the ultrasonic bath 2 and propagating through the electrolytic bath 1 speed up the production of the substances mentioned above and facilitate their penetration in the micropores and cracks or macropores of the ore particles.

During the electrolytic processing of the ore, chlorine and other gases and/or soluble salts are produced near the anode, which penetrate the ore particles contained in the corresponding ore container 30. These gases and/or soluble salts will participate to the disintegration of the ore particles in a next step of the method.

At the same time, hydrogen is produced near the cathode, thereby locally increasing the concentration of heavy water, i.e. of deuterium and/or tritium in particular, that penetrates the macro- and micropores of the ore particles contained in the corresponding ore container 30, this penetration being enhanced under the effect of the ultrasonic bath 2.

Regularly alternating the polarity of the DC voltage applied to the electrodes 3 thus ensures that the ore particles of both ore containers 30 will be penetrated by similar quantities of the same substances.

In a variant embodiment of the method of the invention, reactive metal chlorides, for example sodium, calcium, potassium, etc., are included in the composition of the electrolytic bath 1. Alkaline reactions then take place near the cathode, which generates an at least partial disintegration the ore particles contained in the corresponding ore container 30.

As mentioned further above, the ultrasonic bath 2 enhances the penetration of the substances produced near the cathode into the macro- and micropores of the ore particles contained in the corresponding ore container 30. At the same time, free hydrogen atoms are absorbed by platinum group metals (PGM) present in the ore particles, whereas this absorption is drastically increased by the ultrasonic bath 2.

The electrolytic processing of the ore particles, enhanced by the ultrasonic bath 2 and preferably comprising a number of alternated cycles, cleans and fills the macro- and micropores of the ore particles with substances generated in the electrolytic bath 1, thereby preparing the ore particles for a next step of the method of the invention.

This next step is schematically illustrated in FIG. 2. The prepared ore particles, which were submitted to the electrolytic bath enhanced by ultrasonic bath in a previous step of the method, are placed in a crucible 5. The crucible 5 is preferably made of magnetite powder and fire clay. The crucible 5 containing the ore particles is introduced into an oven 4, preferably a microwave oven, for shock heating of the ore particles, i.e. the ore particles are subjected to a very fast and important temperature increase. The temperature of the ore particles is for example elevated to a temperature between 200 and 300° C. within 60 to 180 seconds, preferably to 250° C. within 120 seconds.

Shock heating of the ore particles is preferably performed in a microwave oven. Submitting the prepared ore particles to high power microwave radiations provokes high excitation of the heavy, semi-heavy and light water molecules in the ore particles, thereby rapidly increasing their temperature. Other technologies are however possible within the frame of the invention for shock heating the ore particles.

Through shock heating, steam is rapidly produced from the heavy, semi heavy and light water contained in the macro and micro pores of the ore particles, which induces high pressure in the macro- and micropores of the ore particles. The rapid increase of pressure makes the ore particles explode, thereby provoking their at least partial disintegration, which releases nanoparticles of noble metals contained therein.

During shock heating, the PGM also release the previously absorbed hydrogen at a high pressure, which also participates to the disintegration of the ore particles and to the release of nanoparticles of noble metals.

If, according to a variant embodiment, reactive metal chlorides were used in the electrolytic bath, then, during shock heating, different salts, including for example bicarbonates, and alkalines which have dissolved in the electrolyte bath and have penetrated the macro- and micropores of the ore particles react with ore substances causing various chemical reactions. As a result of these chemical reactions, some ore substances become soluble, thereby further participating to the disintegration of the ore and the release of noble metals.

The shock microwave heating process for example lasts fifteen minutes at a microwave frequency of 2.45 GHz, the input power of the microwave radiation depending on the quantity of ore particles in the oven.

According to the method of the invention, the disintegrated ore particles and the released nanoparticles are submitted to a next step of separation of noble metals from the remaining ore, preferably to a mechanical step of separation. This step of separation according to a preferred embodiment of the invention is schematically illustrated in FIG. 3.

According to this preferred embodiment, the step of separation uses gravity separation enhanced by ultrasounds. The disintegrated ore, preferably together with the remaining content of the crucible used for shock heating, is put into a preferably cone shaped container 7 made of a permeable material, for example a microporous nylon membrane. The filled cone shaped container 7 is placed into an ultrasonic bath 6, preferably with its tip oriented towards the ground, for an ultrasonic induced gravity separation of the noble metals. Under the effect of the ultrasonic waves, the content of the container 7 is slightly agitated, and the noble metals and other by products tend to sink to the tip of the container 7, while the remains of the disintegrated ore particles are pushed towards the top.

Other separation technologies, preferably mechanical technologies, are however possible within the frame of the invention. In a variant embodiment, for example, separation of noble metals and other byproducts from the remains of the disintegrated ore particles is made through centrifugation of the crucible's content. Separation can also be performed with the help of electrostatic, magnetic and/or chemically-based techniques.

After the completion of the disintegration of the ore particles, the remaining liquid from the electrolytic bath 1 and from the ultrasonic bath 6 and also the sludge, i.e. the remains of the disintegrated ore particles, are preferably tested for the presence of noble metals that are for example collected, i.e. separated, using similar or other separation techniques.

The method of the invention for the recovery of noble metals and other byproducts by disintegration of ore using nontoxic multi-step processing allows for a very high recovery rate (95-99.9%) and does not use any toxic substances like cyanide or mercury, thereby being environmentally friendly. 

1. Method for the recovery of noble metals comprising the steps of: subjecting ore particles to an electrolytic bath enhanced by an ultrasonic bath, said electrolytic bath comprising heavy and/or semi-heavy water, shock heating said ore particles for disintegrating said ore particles, separating noble metals from the remains of said disintegrated ore particles.
 2. Method according to claim 1, wherein said step of separating comprises gravity separation enhanced by ultrasounds.
 3. Method according to claim 1, further comprising the preliminary step of crushing ore for producing said ore particles.
 4. Method according to claim 1, further comprising the preliminary step of centrifuging said ore particles.
 5. Method according to claim 1, wherein the step of subjecting ore particles to an electrolytic bath enhanced by an ultrasonic bath comprises immersing said ore particles in said electrolytic bath, wherein said electrolytic bath is placed inside said ultrasonic bath.
 6. Method according to claim 1, wherein the step of subjecting ore particles to an electrolytic bath enhanced by an ultrasonic bath comprises placing said ore particles in ore containers, wherein said ore containers are placed around electrodes of said electrolytic bath.
 7. Method according to claim 6, wherein said ore containers are cone-shaped.
 8. Method according to claim 6, wherein the external walls of said containers are made of a microporous nylon membrane.
 9. Method according to claim 1, wherein the step of subjecting ore particles to an electrolytic bath enhanced by an ultrasonic bath comprises alternating the polarity of DC voltage applied to electrodes of said electrolytic bath.
 10. Method according to claim 1, wherein said step of shock heating is a step of microwave shock heating.
 11. Method according to claim 1, wherein said step of shock heating comprises placing said ore particles in a crucible in a microwave oven and applying microwave radiation inside said microwave oven.
 12. Method according to claim 7, wherein the external walls of said containers are made of a microporous nylon membrane. 